The present invention relates to the production of butene-1 homopolymers and copolymers with minor amounts of one or more other .alpha.-alkenes in a liquid inert distributing agent or solvent in the presence of Ziegler coordination catalysts.
Ziegler coordination catalysts for the polymerization of .alpha.-alkenes are well known to those in the art, and are typically based upon one or more compounds of metals of groups IV B, V B, VI B of the Periodic table, and one or more organometallic compounds of metals of group I, II, or III of the Periodic table. Many variations of the Ziegler coordination catalysts are known, including, for instance, supported catalysts, catalysts systems which contain additional compounds such as, for instance, Lewis bases and other compounds. All of the known polymerization catalysts of this type may be used in the present process.
The polymerization of butene-1 in the presence of Ziegler coordination catalysts yields both isotactic polybutene-1 and atactic polybutene-1. It is generally desired to obtain polymers having the highest possible isotactic polymer content, and therefore the catalyst composition will generally be chosen so that a high content of isotactic material in the product polybutene-1 is obtained. For instance, a violet titanium trichloride and diethylaluminum chloride are commonly used. The isotactic polybutene-1 is insoluble or only slightly soluble at temperatures below about 45.degree.C in the reaction solvent commonly used for such polymerizations. As known in the art, the reaction solvent is an inert distributing agent or solvent such as pentane, hexane, heptane, gasoline, kerosene and even liquid monomer. Normally, the polymerization in liquid monomeric butene-1 is conducted under superatmospheric pressure.
As noted above, isotactic polybutene-1 is at most only slightly soluble in the conventional reaction solvent at temperatures below about 45.degree.C. The polymerization of butene-1 at temperatures below 45.degree.C or so will normally yield directly a suspension of polybutene which, depending upon the particular reaction temperature chosen, is swollen to various degrees. Because of the effect on polymerization rate, the polymerization temperature is normally chosen as high as possible and thus suspension polymerization reactions are normally conducted at temperatures of about 40.degree.-45.degree.C. As such elevated suspension polymerization temperatures, however, quite swollen, sometimes even jelly-like, polybutene-1 polymers are obtained, and these polymers are most difficult to handle. To overcome some of the problems which are encountered if suspensions of swollen polymers are processed, or further worked up, special types of stirred reactors have been proposed in German patent application No. 1,910,482 (open for public inspection).
If polymerization is conducted at temperatures in excess of 45.degree.C, such as, for instance, 60.degree. to 80.degree.C, a solution of the polybutene-1 is normally obtained. The polybutene polymer can be isolated from the solution, generally and most suitably by solvent evaporation. If the polybutene-1 solution is cooled to temperatures below about 45.degree.C, a gelatinous mass is obtained which cannot be further processed, or which can be further processed only with great difficulty, and there is therefore no suitable method of isolating the polybutene-1 from the polymerization solution without solvent evaporation. In order for the desired polymerization rates to be obtained, polymerization temperatures of at least 50.degree.C and preferably at least 60.degree.C are normally considered necessary. For this reason, butene-1 is normally polymerized using solution polymerization techniques.